Cupcake Lab

When you bake cakes, cookies, muffins, or pastries, you are often asked to use either baking soda or baking powder in the recipe. Do they behave differently? What is the difference in their composition?

A. Baking Soda

Baking soda, NaHCO 3, is an inexpensive household chemical that is commonly used for a variety of purposes in addition to baking. It is found in many products such as antacid tablets, bath salts, contact lens fluid, eye wash, drain cleaner, foot powder, refrigerator deodorizer, and laundry bluing. It can also be used as a toothpaste, a mouthwash, as a relief from the pain and itch of insect bites, and to retain the color of green.

Baking soda goes by several other names - - sodium bicarbonate, bi-carb, or sodium hydrogen carbonate. It is estimated that the most common brand, the Arm and Hammer brand, is found in 90% of American households. The main consumer of baking soda is the food industry, followed by the fire extinguisher industry.

B. Baking Powder

Baking powder is different from baking soda. Baking powder contains baking soda plus some other chemicals that act as acids when added to water. Note the difference between the two!

       There are two types of baking powder.

1. Single acting (fast acting) baking powders contain NaHCO3 and an acid. The addition of water starts the reaction between the two chemicals which begins to release CO2 immediately. These single acting baking powders are quick acting because the reaction occurs completely at room temperature. Single acting means only one chemical reaction occurs. NOTE: Both of these chemicals contain no aluminum . . .

Example of single acting baking powder is:

Rumford Baking Powder: contains NaHCO3, and a phosphate (the acid)

When single acting baking powders are used, the cake or bread texture is formed before baking. The product should be mixed quickly and baked soon after mixing to avoid excessive loss of CO2.

2. Double acting (slow acting) baking powder contains the slow acting ingredient called “alum” (sodium aluminum sulfate) in combination with tartrates or phosphates. The alum will not react with sodium bicarbonate until it is heated, thus leavening continues while the batter is baking.

Double acting baking powders require both moisture and heat for the total release of CO2. Since CO2 is released in two steps - - at room temperature and then at high temperature - - the name developed because it was inconvenient to bake the product as soon as it was mixed.

Baking powders that contain only alum leave a bitter aftertaste and give a heavy textured baked product. However, if tartrate or phosphate is used in the double acting powder, less alum is required, and the bitter taste is eliminated.

A recent concern about double acting baking powders is the presence of aluminum, which some argue is associated with Alzheimer’s disease. Some also argue that the double acting ingredient is not really necessary to form fluffy cupcakes; the CO2 formed from the single acting is sufficient.

C. Reactions of Baking Soda

1. Ionization (Dissociation) Reaction

In water, baking soda just separates into ions according to the following equation:

NaHCO3 (s) → Na+ (aq) + HCO3- (aq) Equation 1

Note that on the left side of the equation is the reactant(s), which is baking soda in this case. The arrow separates what you have before (reactants, on the left) from the after, the product ( s ) (on the right). Notice that no CO 2 gas is released in this process so carbon dioxide is not a product.

2. Decomposition Reaction

Baking soda can be decomposed by very high heating to form sodium carbonate, Na2CO3, commonly called “soda ash,” and water vapor and carbon dioxide gas.

2NaHCO3 (s) → Na2CO3 (s) + H2O (g) + CO2 (g) Equation 2

NOTE: The heat in an oven is not hot enough to cause this reaction; much higher temperatures are needed.

3. Reaction with Acid (the reaction in baking powders)

Acid solutions neutralize baking soda. For example, a dilute solution of some acid could be neutralized by baking soda as shown in the reaction below. We will use HA as a generic formula for an acid (e.g. HF, HCl, H3PO4, HC2H3O2, etc.). For HCl, the A will correspond to Cl. For HF, the A will correspond to F.

HA (aq) + NaHCO3 (s) → NaA (aq) + H2CO3 (aq) → NaA (aq) + H2O (l) + CO2(g)

Equation 3

This is a double displacement reaction , which we will deal with in a later chapter.

The carbonic acid, H2CO3, is unstable and decomposes into water and carbon dioxide gas.

A simple illustration of the reaction can be carried out at home by adding a little vinegar (which contains dilute acetic acid) to about a half teaspoon of baking soda in a glass. The “foam” produced results from the generation of CO2 gas. This is sometimes used to simulate a volcano in science projects.

D. Reactions of Baking Powder

Carbon dioxide gas is produced when baking powder is mixed with water. The CO2 gas causes dough or batter to rise in a process called “leavening.”

As emphasized before, baking powders contain baking soda plus some other chemicals that produce acid when added to water. We mentioned some of these acids: “cream of tartar”, various phosphates, and “alum.”

Baking soda separates into ions in water (recall Equation 1):

NaHCO3 (s) → Na+ (aq) HCO3- (aq)

The H+ from the acid reacts with the HCO3- and releases carbon dioxide and water. The reaction is an acid/base reaction:

ACID BASE

H+ (aq) + HCO3- (aq) → H2O (l) + CO2 (g) Equation 4

The H+ comes from the acid; the HCO3- is a base.

In summary, the acid supplies the H+ ion and the baking soda supplies the base, HCO3- . This is true in any baking powder.

Another leavening agent is yeast. It is a biological leavening agent which ferments sugar in the dough to produce ethyl alcohol, C2H5OH, and carbon dioxide gas. (This is the same reaction that occurs in the wine making industry or in the production of alcohol fuel.) Chemical leavening agents react more rapidly than yeast and cause the dough to rise in a shorter time.

E. Choice of Baking Soda or Baking Powder